This invention relates to axial thrust movement preventing means, and in particular, to an end play control system for a dynamoelectric machine. While the invention is described in particular detail with respect to an induction motor, those skilled in the art will recognize the wider applicability of the inventive concepts disclosed hereinafter.
Modern manufacturing techniques and assembly of dynamoelectric machines, for example, induction motors utilized in high volume appliances and the like, often employ die cast parts. Thus, it is prevalent in the motor industry to provide a stator assembly for an induction motor constructed from a plurality of laminations formed from magnetic material. The stator assembly has a central bore opening in it which is sized to receive a rotor assembly including a shaft. Conventionally, the shaft is supported at its ends by suitable bearings contained in motor end shields. The motor end shields typically are of a die cast aluminum construction, and they are mounted directly to the stator core by any suitable means, such as threaded fasteners or epoxy adhesive. General prior practice has been to machine the end shields, at least along the bearing support areas of the end shields. Machining a die cast part is a relatively expensive motor manufacturing procedure.
In the past, roller or ball bearings were used to journal the rotor shaft. More recently, self-aligning sleeve bearing systems have found wide application in such motor structures. Since the stator assembly and rotor assembly must be assembled with respect to one another to provide a minimum air gap between them for proper motor operation, a variety of techniques have been developed to assemble the parts through the use of shims and the like until the motor construction is completed. After the shims are removed, the rotor and stator remain aligned properly with one another through the now completed motor structure. Self-aligning bearings are particularly well adapted for this kind of construction technique because the motor parts, including the bearing structure, can be moved relative to one another during motor manufacture, the self aligning bearings thereafter attaining proper alignment with the motor shaft without further effort on the part of the motor manufacturer. Self-aligning bearings also eliminate the need for extensive machining of the end shields.
While self-aligning bearings work well for their intended purposes, in some motor applications severe axial forces are applied to the motor shaft, such as during transport or installation of the motor, which can damage the self-aligning bearings of the motor which, in turn, can lead to malfunction of the motor and shortened service life. For example, in dishwasher or disposal appliance applications, the motors often have their rotor and shaft placed vertically. It is known that the energization of the stator windings of the motor will tend to pull or align the rotor within the axial bore through the stator. These two factors often mean that any end play in the bearing sturcture permits excessive rotor assembly movement, which results in severe wear to the bearings and eventual failure of the motor. Conventionally, ball bearings have been used on at least one end of the motor structure. Axial impact forces applied to the motor shaft due to handling can be quite excessive, so that even ball bearings can fail. These axial impact forces acting on prior art self-aligning bearings can overstress the bearing retaining springs and drive the bearing out of its seat or race. While ball bearing structures have been employed in the environment described, manufacturing techniques required for their use include end shield machining. They consequently are more complicated and time consuming to manufacture, and thus are more expensive than motor designs empolying self-aligning bearings at both rotor assembly supporting points.
Other motor applications (e.g., applications employing split phase induction motors employing a motor starting switch for de-energizing the start winding upon the attainment of a predetermined speed of the rotor) are dependent upon the position of a centrifugal actuator for actuation of the switch. Excessive end play in the design of the motor bearing system can misposition the centrifugal actuator so that the motor switch operates improperly thus resulting in motor failure. This is a particularly acute problem with die cast aluminum end shields, which , as indicated above, preferably are not machined for economy of manufacture. One prior art solution has been to employ ball bearings on the switch end of the motor so that the axial dimensions with respect to the switch operating mechanism are controlled effectively.
A number of spring loaded systems have been proposed in which some type of spring structure is employed in an effort to reduce end play in self-aligning bearings. While spring loaded systems work for their intended purpose, they also impose friction losses which adversely affect motor efficiency. Also, when motors employing these self-aligning bearing restraining springs are subjected to excessive axial loading, the springs may be overstressed so that the springs do not properly bias their bearings in their races. This, in turn, can lead to premature failure of the bearing.
The invention disclosed hereinafter overcomes these prior art deficiencies and enables a motor manufacturer to employ self-aligning bearings on both ends of the motor structure by controlling end play within an acceptable range. The invention also enables the motor to withstand considerable handling forces with no functional impairment to the bearing system or axial misalignment of switch components. It further allows close control of end play in a simple self-aligning bearing motor without excessive frictional losses as are encountered with spring loaded systems previously proposed in the prior art.
One of the objects of this invention is to provide a simplified end play control system for dynamoelectric machines.
Another object of this invention is to provide an end play control system for a motor employing self-aligning bearings on each end of the motor structure.
Another object of this invention is to provide an end play control system having low frictional losses.
Another object of this invention is to provide a low cost control system capable of accurately positioning a centrifugal actuator in a motor without a machined stator or end shield.
Another object of this invention is to provide a low cost simplified motor bearing system.
Another object of this invention is to provide an end play control system capable of withstanding large axial loads on the motor shaft.
Other objects of this invention will be apparent to those skilled in the art in light of the following description and accompanying drawings.